1. Field of the Invention
The present invention relates to a steam turbine test facility for performing tests for performance and reliability verification of a steam turbine plant, a low-load test method using the steam turbine test facility, and a load dump test method using the same.
2. Description of the Related Art
Conventionally, a steam turbine test facility is provided to evaluate the performance of a steam turbine plant constituting a part of a thermal power plant or a nuclear power plant. Such a steam turbine test facility includes a test steam turbine. The test steam turbine is used to simulate the behavior of a steam turbine installed in the steam turbine plant in such a manner that any particular one of a high-pressure turbine, a medium-pressure turbine, and a low-pressure turbine of the steam turbine plant is operated on a simulation basis. The steam turbine test facility performs performance and reliability verification tests such as a high-load test and a low-load test to evaluate the performance and reliability of the test steam turbine, thus evaluating the performance and reliability of the steam turbine plant.
(1) High-load Test
In the high-load test in which the power obtained by steam exceeds mechanical loss, the test steam turbine can increase and maintain its rotational speed by itself. In the high-load test, therefore, a generator and a dynamometer are connected to the test steam turbine to collect the output power. This test is performed to measure necessary data to evaluate the performance and reliability of the steam turbine plant. The data to be measured includes stress generated in a rotor blade, a steam flow in the steam turbine, and so on.
(2) Low-load Test
When the load (steam flow rate) on the steam turbine falls to a fixed value or below and the steam turbine has long rotor blades (for example, in the case of a low-pressure turbine), a steam vortex flow may develop on the downstream side thereof, thereby generating random vibration on the steam turbine. In view of this, the low-load test is performed to evaluate the reliability of the steam turbine plant inclusive of effects that is produced by such random vibration.
The low-load test is performed to measure necessary data to evaluate the performance and reliability of the steam turbine plant when the load on the test steam turbine is equal to or lower than the load at which random vibration occurs (that is, in a low-load state). The data to be measured includes stress generated in a rotor blade, a steam flow in the steam turbine, and so on. In the low-load test, if the power obtained by steam falls below mechanical loss, the test steam turbine cannot maintain its rotational speed by itself. To cope with such inconvenience, conventionally, a drive turbine and a motor are connected to the test steam turbine to maintain the rotational speed of the test steam turbine.
(3) Load Dump Test
The load dump test during which the load on a nuclear reactor and a steam turbine is disconnected is performed in a nuclear power plant. When the load on the steam turbine is disconnected, the pressure in the steam turbine suddenly decreases to cause the steam extracted from the main steam to flow reversely (flashback), thereby generating an unsteady steam flow inside the steam turbine. A fluid force resulting from this unsteady steam flow creates an exciting force and thus flashback vibration occurs on the rotor blades.
Further, as proved in recent years, when the main steam is interrupted, the steam turbine enters an extremely low load state, the steam vortex flow generates random vibration, and the random vibration is superimposed on flashback vibration, with the result that a large vibration force occurs on the rotor blades.
Then, in order to evaluate the reliability of the steam turbine plant inclusive of effects that is produced by the flashback vibration and random vibration in the load dump test, it is desirable to perform the load dump test by using the steam turbine test facility.
As described above, the high-load test is performed in such manner that a generator and a dynamometer are connected to the test steam turbine to collect the generated power. On the other hand, the low-load test is performed in such manner that a drive turbine and a motor are connected to the test steam turbine to maintain the rotational speed of the test steam turbine.
However, it is known that in the load dump test, immediately after the load is disconnected (that is, the generator load is disconnected), the rotational speed of the actual steam turbine temporarily rises (overspeed).
On the other hand, the behavior of the test steam turbine appearing after disconnection of the load does not coincide with that of the actual steam turbine because they are different in inertia. Even when a drive turbine and a motor are connected to the test steam turbine so as to maintain the rotational speed with the load disconnected (that is, in a load disconnection state), it is not possible to precisely simulate transitional changes of the rotational speed of the actual steam turbine. For example, the transitional changes include overspeed generated immediately after the load on the actual steam turbine is disconnected.
Specifically, with the conventional test steam turbine to which a common drive turbine and a motor are connected, it is not possible to precisely simulate the behavior appearing when the load on the actual steam turbine is disconnected.
Therefore, with the conventional test steam turbine, it is not possible to accurately evaluate an influence of flashback vibration and random vibration generated when the load is disconnected.
A generator and a dynamometer are connected to the test steam turbine in the high-load test while a drive turbine and a motor are connected to the test steam turbine in the low-load test and the load dump test. Therefore, it is necessary to change devices to be connected to the test steam turbine each time the high-load test, low-load test, or load dump test is performed. This will decrease the efficiency of tests for performance and reliability verification, inclusive of the above tests.